36 UNIVERSITY OF MISSOURI STUDIES [224- 



again on August i8 and finally died on August 20. There is no 

 external indication whatever that the regenerated structure, 

 Fig. 30 (n), is segmented. The basal portion (b) represents 

 merely a part of the connection between the regenerated struc- 

 ture and the eye on the opposite side. There is little ground 

 for supposing that, had the individual lived longer, the appen- 

 dage would have become segmented; for more than three 

 months had elapsed between the removal of the eye and the 

 death of the crayfish and two moults had intervened. This is 

 nearly twice as long as the period occupied in the development 

 of the appendage 'described under Type II (Fig. 33, PI. IV), 

 and in the latter case fourteen segments were regenerated. 



The horn-like processes of Types III and IV agree in the 

 fact that in all instances, the process is directed somewhat for- 

 ward and is usually curved upward and at the same time slightly 

 inward toward the median line. They further agree in the pres- 

 ence of a hard chitinous cuticle and in the absence of setae. 



Type V : Indefinite structure regenerated. Finally there 

 remain to be considered instances in which no definite regener- 

 ation takes place. The number of individuals, which may be 

 considered as belonging to this negative type, are numerous. In 

 the majority of such instances, however, the crayfish died before 

 the occurrence of a moult, or the moult occurred in a very short 

 time after removal of the eye. It is, therefore, impossible to say 

 what the final outcome might have been. In most cases in which 

 the entire eye had been removed, there were no external indi- 

 cations whatever of any regeneration until after a moult, but 

 this is not true of every instance. Fig. 28, PI. IV, shows the 

 normal left eye and the stump from which the right eye was 

 removed four months before. The animal died without having 

 moulted after the operation. The new tissue that had been 

 formed is represented by the shaded portion distal to the line 



